The present invention relates to methods for producing integrated circuit devices and more specifically to a method for forming a bipolar transistor using doped spin on glass (SOG).
Known methods for forming bipolar transistors involve at least two mask, etch, and implant operations in which n-type and p-type impurities are implanted into a collector, typically made of silicon. The base is formed with the first mask, etch, and implant operation. The photoresist layer used during the masking operation is removed and a new photoresist layer is provided before the second implanting operation. The emitter is formed during the second mask, etch, and implant operation. In such a process, the implant energy has to be reduced to produce shallow junctions.
This method suffers from the disadvantage that implanting produces defects which lie in the space charge region of the junction. The implanted impurity is brought to rest by an inelastic collision with silicon atoms in the crystal lattice, which damages the crystal lattice structure by knocking silicon atoms out of place. The crystal lattice structure must be epitaxially regrown by a thermal anneal to activate the implanted impurities by incorporating them into the crystal lattice. For shallow junctions, a rapid thermal process (RTP) cycle is typically performed. The damage from implanting is not totally repairable without causing undesirable enhanced diffusion of the impurities which is inconsistent with shallow junction technology. Defect sites having energies in the middle of the band gap remain and produce a conduction path which ultimately causes a leakage current to flow.
Therefore, it would be desirable to provide a process for forming a bipolar transistor, which does not suffer from the disadvantages of known process steps.